The present invention relates to a method, in particular an in vitro method, for identifying specific immune cells, in particular MDSCs, comprising analyzing a modification, preferably the methylation status,of at least one CpG position in the mammalian gene region for endoplasmatic reticulum-golgi intermediate compartment 1 (ERGIC1), wherein a demethylation or lack of methylation or modification of said gene region is indicative for an MDSC, when compared to a non-MDSC. The analyses according to the invention can identify specific sub-populations of MDSCs, namely monocytic MDSCs (m MDSCs) on an epigenetic level and distinguish them from all other cells in complex samples, such as, for example, other blood or immune cells. The present invention furthermore provides an improved method for quantifying m MDSCs, in particular in complex samples. The method can be performed without a step of purifying and / or enriching cells, preferably in whole blood and / or non-trypsinized tissue.